Major deltas of the world
Future delta projections
Explore the projections of future climate and socio-economic change for the world's major deltas in the Google Map below. These projections were obtained from studies by Utrecht University and the Intergovernmental Panel on Climate Change (IPCC).
Details on the origin and computation of projections can be found below.
Projections of temperature change (in °C) were obtained from the IPCC’s Sixth Assessment Report (AR6) from 2021. They are shown for the period 2081-2100 relative to 1850-1900 for the three scenarios SSP1-2.6, SSP2-4.5 and SSP5-8.5. For 50 deltas, changes in temperature were visually assessed from the IPCC’s interactive atlas.
Projections of precipitation change (in %) were obtained from the IPCC’s Sixth Assessment Report (AR6) from 2021. They are shown for the period 2081-2100 relative to 1850-1900 for the three scenarios SSP1-2.6, SSP2-4.5 and SSP5-8.5. For 50 deltas, changes in precipitation were visually assessed from the IPCC’s interactive atlas.
The population projections are based on a study by Jones and O’Neill (2016). They show the total population for the period 2020-2100 in 10-year time intervals for SSP1, SSP3 and SSP5 at a resolution of 7.5 arc minutes (~15 km at the equator). They were produced by using a gravity-type model, reflecting spatial change based on density and contiguity of population concentrations. The model was calibrated with historic data from 1990-2000 to estimate parameters for all SSP scenarios and downscale the population number per country and scenario. Population density for individual deltas was calculated from grid cells within the delta boundaries of Dunn (2017) adapted from Tessler and others (2015).
The urbanization projections are based on a study by Gao and O’Neill (2020). They show the fraction of urban land for the period 2020-2100 in 10-year time intervals for SSP1, SSP3 and SSP5 at a resolution of 7.5 arc minutes (~15 km at the equator). For their computation, the two urban simulation models, CLUBS and SELECT, were used to combine estimates of the total amount of new urban land development per country with spatial change of urban land in 375 subnational regions. The models were calibrated with fine-spatial-resolution Landsat remote sensing data from 1975-2014. Urban area for individual deltas was calculated from grid cells within the delta boundaries of Dunn (2017) adapted from Tessler and others (2015).
Projections of sea level rise (in m) were obtained from the IPCC’s Sixth Assessment Report (AR6) using the IPCC's and NASA's Sea Level Projection Tool. They are shown for 2091-2100 relative to the period 1995-2014 for the three scenarios RCP2.6, RCP4.5 and RCP8.5.
The projections show the change in river discharge (in %) between the period 2001-2010 and 2051-2060 for the 10%, 50% and 90% percentiles of monthly averages. They were computed by Rens van Beek, assistant professor of large-scale hydrology and earth surface processes, for which he was supported by PBL Netherlands Environmental Assessment Agency. The global hydrological model PCR-GLOBWB and the general circulation model HadGEM2–ES were used with the SSP2 scenario for projections for the period 2001-2010 and the SSP1-2.6, SSP2-4.5 and SSP3-6.0 scenarios for the period 2051-2060. For both periods, a resolution of 30 arc minutes was used (~60 km at the equator).
Further reading
- Van Beek, R. (2018). Freshwater availability. [Scientific justification of the information produced for parts of the chapter ‘Water and food production’ of ‘The Geography of Future Water Challenges’ (2018), Utrecht: PBL Netherlands Environmental Assessment Agency].
Projections of fluvial sediment flux originate from a study by Frances Dunn, postdoctoral researcher on fluvial sediment delivery to deltas, and others. They show the changes in fluvial sediment delivery (in %) to 47 of the world’s major deltas between the 30-year periods at the start (1990–2019) and end (2070–2099) of the present century for the SSP1-2.6, SSP2-4.5 and SSP3-8.5 scenarios. To compute the projections, Frances Dunn and colleagues used the hydrogeomorphic model WBMsed, at 6 arc min spatial resolution (~11 km at the equator), with a range of environmental change scenarios that include the impact of future climate change, dam construction, population and wealth.
Further reading
- Dunn, F. E., Darby, S. E., Nicholls, R. J., Cohen, S., Zarfl, C., & Fekete, B. M. (2019). Projections of declining fluvial sediment delivery to major deltas worldwide in response to climate change and anthropogenic stress. Environmental Research Letters, 14(8), 084034.
Historic subsidence projections
Gilles Erkens, researcher in land subsidence and geomorphology, and Edwin Sutanudjaja, researcher in model development, compiled a global subsidence map for the period 2000–2014. Their approach exclusively focussed on aquifer abstraction-induced land subsidence. For the computation, they used the integrated global hydrological and water resources model PCR-GLOBWB to simulate monthly groundwater head changes which were fed into the land subsidence module iMOD-SUB-CR. Both models use a spatial resolution of 5 arc minutes (~10 km at the equator).
Further reading
- Erkens, G., & Sutanudjaja, E. H. (2015). Towards a global land subsidence map. Proceedings of the International Association of Hydrological Sciences, 372, 83-87.
Future subsidence projections
A study by Herrera-García et al. (2021), with contributions from Gilles Erkens, projected the risk of subsidence worldwide in 2040 by identifying environmental conditions, that favour land subsidence, and anthropogenic factors that lead to groundwater depletion. This combination of subsidence susceptibility and probability of groundwater depletion was used to estimate a “proxy” of potential subsidence hazard which ranges from very low, low, medium low, medium high, high to very high. In the study, they applied a global change scenario based on steady population growth and increasing greenhouse gas emissions (SSP2-8.5).
Jaap Nienhuis, assistant professor of coastal morphodynamics, and Roderik van de Wal, professor of sea-level change and coastal impacts, applied a morphodynamic model to investigate land-area change of 6,402 deltas worldwide for the period 2081-2100 for the RCP2.6, RCP4.5 and RCP8.5 scenarios. The model compares suspended sediment supply against subsidence and sea-level rise (together relative sea-level rise). Based on the present-day delta area and delta thickness, it predicted future shoreline retreat or advance. The model was validated using remote-sensing observations of delta change from 1985-2015.
Further reading
- Nienhuis, J. H., & Van de Wal, R. S. (2021). Projections of global delta land loss from sea‐level rise in the 21st century. Geophysical Research Letters.
Maria Santos and Stefan Dekker, professor of global eco-hydrology and sustainability, developed a new framework which shows when deltas started to degrade and became locked-in, i.e. when reversing the current system to a natural system is extremely costly, if feasible at all. They tested the framework for 48 of the world’s largest deltas by examining the coupling between population and agricultural land-use development over the period 1700-2010. Adding this historical perspective provides insights in the pathways of delta development by identifying how legacy effects can hinder current and future adaptation and resilience of deltas.
Further reading
- Santos, M. J., & Dekker, S. C. (2020). Locked-in and living delta pathways in the Anthropocene. Scientific reports, 10(1), 1-10.